1. Field of the Invention
The present invention relates to an air bag system for a vehicle to protect an occupant.
2. Description of the Related Art
Conventionally, there has been known an air bag system for a vehicle that is inflated and expanded by gas supplied from an inflator to constrain an occupant's movement so as to protect him or her at the time of a collision of the vehicle.
In such an air bag system for a vehicle, it has been proposed to provide a vent hole (discharge port) on an air bag (bag body), through which gas is discharged into the air bag.
JP H06-286569 A discloses, for example, an air bag system for a vehicle, in which, in order to reduce impact of an air bag onto an occupant when the occupant hits the air bag inflated and expanded, there is provided a slot-like vent hole and an elastic member provided across the vent hole, so that each end of the elastic member is fixed onto the air bag.
When an inflated and expanded air bag comes in contact with and presses an obstacle and the like, it is preferable to restrain inflation and expansion of the air bag by increasing the discharging rate of gas in the air bag from the vent hole. However, a conventional air bag system for a vehicle, as disclosed in JP H06-286569 A, discharges gas in the air bag from the vent hole at an approximately constant rate even when the inflated and expanded air bag comes in contact with and presses an obstacle, and discloses or suggests nothing about regulation of discharging rate of gas in the air bag.
In the air bag system disclosed in JP H06-286569 A, gas filling the air bag is constantly leaked from the vent hole during the process of inflating and expanding the air bag, which delays sufficient increase of internal pressure of the air bag by the leaked gas amount, taking more time to blow up the air bag, and consequently to hinder a quick inflation and expansion of the air bag.
In addition, it is preferable to maintain gas pressure in the air bag until an occupant is sufficiently restrained by the inflated and expanded air bag. However, the conventional air bag system for a vehicle disclosed in JP H06-286569 A keeps the vent hole open even during the inflation and expansion of the air bag, thus it is difficult to maintain the gas pressure in the air bag at a constant rate, which sufficiently restrains the occupant.
In the light of the above various difficulties, the present invention has an object to preferably regulate discharging rate of gas filling in an air bag body from a vent hole when the air bag body comes in contact with and presses an obstacle and the like during the inflation and expansion of the air bag body, but quickly expand the air bag body with the vent hole closed if not coming in contact with the obstacle as well as maintaining the gas pressure in the air bag body at a constant rate.